A theorem is an important mathematical result that has been proved to be true. The proof must be based on confirmed mathematical facts.

The stamp commemorates a famous theorem called "Fermat's Last Theorem" that British mathematician, Andrew Wiles, proved in 1994. This theorem states that, if \(n\) is greater than \(2\), then there are no whole numbers \(x,y,\) and \(z\) such that \(x^n + y^n = z^n\). In 1637, Fermat scribbled this result in the margin of one of his notebooks, stating that he had a proof, but that it was too long to fit in the margin of his notebook. The result fascinated mathematicians for three and a half centuries. Andrew Wiles' proof is way too long to fit in the margin of a notebook!

Some other important theorems that you may have heard of are

• Pythagoras' theorem
• The Fundamental Theorem of Algebra
• The Extreme Value Theorem
• The Intermediate Value Theorem
• The Mean Value Theorem
• The Fundamental Theorem of Calculus

Mathematicians reserve the name "theorem" for results that are very important. Results that are less important are called "Propositions". "Lemmas" are little results that help mathematicians to prove a theorem or proposition.